This invention relates to electrochemical cells, and particularly to such cells having a complex cover formed by being highly cold worked into the special configuration.
Cells of the type in U.S. patent application Ser. No. 102,814, now U.S. Pat. No. 4,931,368 assigned to the assignee herein, employ a complexly configurated cell cover which is highly cold worked in its formation The center of the cover preferably is specially configurated to incorporate a safety vent arrangement. This cold working of the cover includes a rollback which engages the outer peripheral gasket. The cold worked cover has high strength enabling it to continuously press the seal tightly against the outer cell housing. Such a seal has been found effective and desirable.
Unfortunately, cold worked steel and the like is highly subject to corrosion. The work hardened metal in areas highly cold worked and not cathodically protected is subject to excessive corrosion such as when the external cover surface is exposed to high humidity or other environments tending to naturally cause corrosion. Excessive rusting of the external cover surfaces is observed, for example, when cells are stored in high humidity test cabinets.
Conceivably the highly cold worked metal could be annealed and thereby rendered resistant to corrosion. However, that was not possible because the annealing process would reduce the yield point and the elastic deformation or recovery of the rollback. This in turn would reduce the radial displacement of the tangential spring of the unit and thereby reduce the ability of the resulting seal to remain leak free over its wide temperature range.